The liver synthesizes both exportable and non-exportable proteins. We are studying how the liver can differentiate between these two classes of proteins and how the liver transports these different proteins from their site of synthesis on cytoplasmic polysomes to their final location either inside or outside of the cell. To elucidate some of the mechanisms by which the liver cell accomplishes this, we are studying the following topics: (a) The attachment of polysomes, active in the synthesis of secretory proteins, to the endoplasmic reticulum membrane. (b) The effect of colchicine on the secretion of plasma proteins. (c) The biosynthesis of albumin.